The findings published in the international journal 'Astrophysics and Space Science' state that the cometery fragment contained dense collection of red cells.

Commenting on the study at a press conference here, Dr N Chandra Wikramesinghe, Director of Cardiff Centre for Astrobiology, UK, said "what makes this study most important is the similarity of the red particles with living cells."

"If the red rain cells are finally proved to be of extra-terrestrial origin then that would be one of the most important discoveries in human history. It will change our concept about the universe and life," he added.

The red-coloured rains were reported in different parts of Kerala from July to September 2001.

About a million comet and interstellar dust particles - most smaller than the width of a human hair - are believed to be inside a sealed canister.

The particles, captured in 2004, are thought to be pristine leftovers from the birth of the solar system about 4.5 billion years ago. Some samples could be even older than the sun.

The next stop for the capsule was the Johnson Space Center in Houston, where scientists unlocked the canister. After a preliminary examination, they shipped the particles to laboratories all over the world for further study to analyze their composition.

"Inside this thing is our treasure," said principal mission scientists Don Brownlee of the University of Washington.

Stardust's successful return was welcome news to the space agency, which suffered a setback in 2004 when its Genesis space probe carrying solar wind atoms crashed into the same Utah salt flats and cracked open after its parachutes failed to deploy.

After the Genesis mishap, engineers rechecked Stardust's systems. Duxbury said its return home went "like clockwork".

The Stardust mothership released the shuttlecock-shaped capsule, which plunged through the atmosphere at 29,000 mph.

The first parachute unfurled at 100,000 feet, followed by a larger chute, which guided the capsule to a 10-mph landing at Dugway Proving Ground. There was a tense moment in mission control when engineers could not immediately confirm the first parachute had opened.

Before coming to rest on its side, the capsule bounced three times but didn't crack, said Joe Vellinga of Lockheed Martin, who helped lead the recovery.

Scientists in white protective suits spent the day cleaning the capsule and its canister of dust samples before the trip to Johnson Space Center.

The Stardust mothership remained in orbit around the sun and NASA is considering sending it to another comet or asteroid to snap photos. There won't be another chance for a sample return, however, because the craft carried only one capsule.

Stardust and Genesis were the first robotic retrievals of extraterrestrial material since the unmanned Soviet Luna 24 in 1976, which brought back lunar rocks and soil.

The Stardust spacecraft was launched in 1999 and has traveled nearly 3 billion miles, including three loops around the sun.

In 2004, it survived a hazardous trip through the comet's coma, a fuzzy halo of gas and dust, to snatch the cosmic dust with a tennis racket-sized collector mitt. Along the way, it also scooped up interstellar dust - tiny particles thought to have been thrown out by stars that long ago exploded and died.

During the comet flyby, the spacecraft also beamed back 72 black-and-white pictures showing broad mesas, craters, pinnacles and canyons on the surface of Wild 2.

Six months ago, NASA sent the Deep Impact probe into the path of another comet. The probe's high-speed collision with comet Tempel 1 set off a celestial fireworks display and bared the comet's primordial interior.

Scientists have been analyzing the voluminous debris hurled from the comet and are trying to figure out the size of the crater caused by the debris-shrouded impact.